The proposed work integrates two approaches to understanding how children learn meanings of words and develop theories about the world: a focus on the individual-child and a focus on the sociocultural context of development. Children's understanding of names for objects, emotions, and physical changes of state are explored by examining how word meanings are negotiated in conversations with parents and siblings. Similarly- children's causal theories about emotion and change of state are explored by examining explanations that are constructed within conversations Finally, the social and cultural context of this work is expanded by including families of Mexican descent in addition to families of European descent. Children's understanding of these concepts and theories in spontaneous conversations are an important foundation for later social competence and scientific thinking.